1. Field of the Invention
The present invention relates to a power output apparatus provided with an engine including a combustion chamber or the like, and a hybrid power output apparatus including the engine and a motor generator apparatus. Moreover, the present invention also relates to a method of controlling the engine, a method of controlling the hybrid power output apparatus, and a hybrid vehicle including the above-described hybrid power output apparatus.
2. Description of the Related Art
In order to purify gas emitted from an engine, there is provided an exhaust gas purification apparatus having a suitable catalyst. Such an exhaust gas purification apparatus, and specifically a ternary catalytic apparatus, for example, can remove harmful substances, such as CO, NOx, HC, or the like, and thus does not cause so-called environmental pollution.
In the ternary catalytic apparatus, it is necessary to pay attention to the deterioration of the catalyst. That is because the catalyst deterioration does not allow the apparatus's effective function of removing the harmful substances. It is known that as an atmosphere around the catalyst reaches a higher temperature which is one condition, or oxygen around the catalyst becomes more excessive which is another condition, this catalyst deterioration generally tends to occur more frequently. It is also known that the catalyst deterioration is substantially accelerated if the both conditions occur simultaneously. The latter condition out of them, i.e. to be an atmosphere with excess oxygen, has substantially the same meaning as that an air/fuel mixture becomes lean (i.e. to be in the condition that the amount of air is relatively greater than that of fuel, as compared with an ideal air/fuel ratio), considering that the exhaust gas purification apparatus is mounted on the middle of an exhaust tube directly connected to an engine, which is, in other words, to be a lean atmosphere.
Incidentally, according to one explanation, the reason why the catalyst deterioration occurs in such an atmosphere is considered as follows: platinum particles constituting the catalyst grow greatly in the atmosphere and reduce their surface areas, thereby reducing the opportunity for the exhaust gases to be in contact with the catalyst.
The catalyst deterioration as described above, or the appearance of an environment that promotes this deterioration, may occur frequently. For example, in typical gasoline engines or the like, fuel cut control (or merely referred to as “fuel cut”, “F/C”, or the like) is sometimes performed in order to improve the fuel consumption, to prevent an excess load, or the like. In this case, the ratio of fuel in the air/fuel mixture decreases and the ratio of air increases, so that the above-described lean atmosphere appears. Therefore, if no countermeasures are taken in this case, that accelerates the catalyst deterioration.
For the purpose of dealing with such a problem, even now there is provided a method of prohibiting the execution of the fuel supply stop control or the like if the temperature of the catalyst is higher than a predetermined value, in order not to expose the catalyst to the lean atmosphere on the premise of typical engines, as shown in Japanese Patent Application Laying Open NO. Hei 8-144814, for example.
Incidentally, it is known that the exhaust gas purification apparatus is also mounted on a so-called hybrid power output apparatus, which has the above-described engine and a motor generator apparatus and is tried to have a functional association between them, as shown in Japanese Patent Application Laying Open NO. Hei 9-47094, Japanese Patent Application Laying Open NO 2000-324615 or the like, for example. In such a hybrid power output apparatus, the control as described in Japanese Patent Application Laying Open NO. Hei 8-144814 can be executed.
However, there are still some insufficient points left in the countermeasure for protecting the catalyst deterioration, as disclosed in the above-described Japanese Patent Application Laying Open NO. Hei 8-144814 or the like. This specifically applies to the above-described hybrid power output apparatus.
In the hybrid power output apparatus of this kind, a battery is charged by using the motor generator apparatus as a generator which is rotated by a driving force of the engine, or by using an exclusive generator included in the motor generator apparatus, which depends on required operating conditions, as occasion demands. Moreover, a drive shaft is rotated independently or together with the engine, by using the motor generator apparatus as a motor, which receives power supply from the battery and rotates, or by using an exclusive motor included in the motor generator apparatus. The power output apparatus of this kind is broadly classified into a parallel hybrid system and a series hybrid system. In the former system, the drive shaft is rotated by one portion of the output of the engine and by a driving force of the motor generator apparatus. In the latter system, the output of the engine is only used for charging by the motor generator apparatus, and the drive shaft is rotated by the driving force of the motor generator apparatus.
In the hybrid power output apparatus as described above, the role of the engine is relatively reduced, so that it is possible to achieve a remarkable effect, such as decreasing the fuel consumption, decreasing the concentration of the harmful substances in the exhaust gases, or the like.
At the same time, however, there is a possibility that an undesired situation may happen in the hybrid power output apparatus from the viewpoint of the catalyst deterioration. This is because the engine is sometimes operated intermittently if the drive shaft is rotated by the cooperation of the motor generator apparatus and the engine, as described above. In this case, the engine is operated such that, after a certain operating period, it enters a down period for the time being, and then again enters an operating period. In this case, especially at a transition time point of transmitting from the operating period to the down period, since fuel injection is once stopped, the amount of air relatively increases. This means that the lean atmosphere appears, so that the catalyst deterioration can be possibly accelerated. Moreover, at the same time point, there is definitely an idle period of the engine, and it is basically impossible to restrict air flow to the exhaust tube due to the idle, so that there is a possibility that a leaner atmosphere may appear.
Furthermore, the above-described intermittent operation is considered to be performed when the engine is warm or when it has a high load, so that the catalyst is exposed even to a high temperature atmosphere. According to this, it can be said that the catalyst deterioration occurs more easily.
As described above, the hybrid power output apparatus may have a problem that it increases the concentration of the harmful substances in the exhaust gases as a result of accelerating the catalyst deterioration at each time of passing through the transition time point of transmitting from the operation period to the down period.